This invention relates to a thermally actuated valve assembly and more particularly to a multi-function thermal vacuum valve useful for instance in automotive emission control systems.
Various thermally actuated valves have been used for automotive applications. For example, wax actuated valves have long been used. These valves consist of a spool valve which is actuated by a volume change of wax upon reaching a predetermined temperature. These valves, however, have drawbacks and limitations. The valves are subject to loss of wax due to high pressure build up and consequently can exhibit a shift in operating temperature and are actuable at only one temperature. Also the spool valve design allows for cross venting when connected to more than one pneumatic source. Additionally they are costly to manufacture.
Thermally actuated valves incorporating bimetallic members as the actuating means such as described in copending application Ser. No. 530,800, entitled Doubled Throw Thermal Valve, filed Dec. 9, 1974, now abandoned, and copending application Ser. No. 641,795, entitled Dual Function Thermal Valve, filed Dec. 18, 1975, now U.S. Pat. No. 4,026,464, each having the same assignee as the present application have also been used. These valves have proved successful but still these valves have the inherent disadvantage for certain applications of allowing possible cross venting. Also the valves cannot be tested prior to final assembly.
Accordingly it is an object of this invention to provide an improved thermally responsive multi-function valve in which cross venting is prevented. It is another object of this invention to provide a thermally responsive multi-function valve in which the functions can be switched simultaneously at one temperature or in sequence at two different temperatures. It is still another object of this invention to provide thermally responsive multi-function valve which can be tested prior to final assembly. It is yet another object to provide a thermally responsive multi-function valve which provides for communication between two separate vacuum sources and two separate activity ports. It is yet still another object to provide a thermally responsive valve which is compact in size, reliable in operation and easy to construct. Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.
Briefly the thermally responsive multi-function valve of this invention comprises a two part valve body, a first part having two pairs of ports extending from the body and a valve switching assembly contained therein and a second part with a central cavity in which the first part is partially housed. The valve switching assembly provides for two chambers isolated one from another in the first valve body. One pair of the ports are positioned to be in communication with each of the chambers thereby providing two passages in the valve body. The passages each have a valve seat contained therein. In the bottom of the cavity in the second part, a support post is disposed upon which a multi-member thermostatic disc assembly is mounted. The assembly comprises two preformed thermostatic discs with a spring member contained therebetween within a disc carrier or housing member. The two disc members are provided to be actuable at different predetermined temperatures. Touching the top of the disc assembly is a motion transfer pin with two valve plug members which extends into the first valve part and valve switching assembly so that a valve plug is positioned to act as a valve seal in each of the chambers. A sealing means with two wiper seals is positioned around the transfer pin to provide isolation between the chambers while still allowing slidable movement of the pin. A spring member biases the pin to be in engagement with the disc assembly.
Initially, in a first temperature range, the transfer pin engages the disc assembly while positioning the first plug or valve seal to engage the first valve seat and thereby block communication in the first passage between the first two ports and positioning the second plug or valve seal to be out of engagement with the second or bottom valve seat thereby providing communication in the second passage between the second two ports. At a second predetermined temperature, one of the discs members snaps to an inverted dish-shaped configuration which causes the first valve plug to move out of engagement with the first valve seat but does not move the second valve seal into engagement with the second valve seat thereby providing communication between the first two ports and the second two ports but not between them. Finally at a third pre-determined temperature, the second of the disc members snaps to an inverted dish-shaped configuration which moves the second valve seal into engagement with the second valve seat thereby only providing communication between the first two ports.